The invention concerns a refraction device for the subjective determination of the spherical and astigmatic sight properties of the eye having a device for beam division into two partial beam paths, whereby at least one sight character is divided in the eye into two comparative images which can be perceived with a look, and an optical device which is associated with the respective partial beam path and which is suitable for setting given optical properties in the two partial beam paths.
Such a refraction device is known from German published specification (DE-AS) No 1 155 615 or from the German journal `Der Augenoptiker`, issue 2, 1967, pages 7 to 10 and 39. In that known refraction device, the optical device used is cylindrical lenses with which the comparative images of the sight character can be made different only by .+-.0.25 diopters. If the eye to be examined has poor eyesight, those minor diopter differences however are scarcely perceptible. A further disadvantage with that known refraction device is that the cylinder axis determination operation involves comparing together lenses whose resulting cylinder axis are unknown to the person carrying out the examination, and whose astigmatic difference is only .+-.0.25 diopters even in the case of the highest cylinders. In addition that known refraction device has a rigid prismatic displacement for dividing a beam into two partial beam paths and is therefore only suitable for the so-called 5-meter viewing distance as an accessory device for a commercially available phoropter. That rigid prismatic displacement only permits an eye examination with a sight character of a visual acuity of 0.6. Smaller sight characters have the result that the comparative images are too far apart and larger sight characters result in overlapping of the comparative images. Both of those however are disadvantageous in terms of exact subjective comparison. A further disadvantage which is not to be underestimated with that known refraction device for simultaneous testing is that for the cylinder axis determination operation, it is necessary for the refraction device to be appropriately turned. As a result however the comparative images lose their association so that the communication between the patient and the person operating the refraction device is impaired or made more difficult. In addition, due to the asymmetrical beam path in that known refraction device one object or comparative image is produced a few centimeters nearer than the other object or comparative image. A further deficiency is that the examination strategy or procedure with that refraction device is just as difficult to learn as with the conventional refraction devices as it is not possible for a user to be guided by means of a computer.
U.S. Pat. No. 4,943,162 discloses a refraction device having a cylinder compensator which forms an accessory device for conventional phoropters. That refraction device is intended to enable a patient himself to adjust his astigmatic defect by the use of two successively arranged Sims lenses, that is to say cylindrical lenses which are arranged in succession. It is not possible with that known refraction device for two comparative images to be simultaneously compared to each other in order in that way to provide for subjective determination of the sight properties of the eye. That means however that the refraction determination operation which is carried out with that refraction device, without comparative images, is probably impossible for a proportion of the order of magnitude of 80% of the normal ophthalmologist public.
U.S. Pat. No. 4,529,280 discloses a near vision device which however is not capable of effecting simultaneous image comparison. It is not possible in that case to provide for determining visual acuity with variable sight characters. The step of ascertaining refraction is effected in accordance with an assessment on the part of the patient who however does not have comparative images simultaneously available. All experience in ophthalmology shows however that with a majority of patients that results in incorrect results. Ophthalmological examination methods are also described for example in the German book by W Straub, Volume II, Ferdinand-Enke-Verlag Stuttgart 1976.
U.S. Pat. No. 4,834,527 describes a device for safeguarding the distance between a patient and an ophthalmological device using the principle of the so-called Non-Contact-Tonometer.